1. Field of the Invention
The present invention relates to a head positioning control device for a magnetic disk apparatus, and more particularly to a head positioning control device for a magnetic disk apparatus, capable of preventing the degradation of accuracy of magnetic head positioning in a device in which a servo area is included in a data recording area of a magnetic disk and a magnetic head is positioned on the basis of servo information read out from the servo area.
2. Description of the Related Art
In a conventional head positioning control device for a magnetic disk apparatus, a timing signal for switching a head address is supplied from a control device regardless of the position of a servo area which is written in a data recording area of a magnetic disk. Further, when a sector period is set correspondingly to a cylinder area, a microprocessor counts pulses generated every time the head passes through the cylinder and modifies the sector period, based on a cylinder address, for positioning the magnetic head. However, the above-described conventional head positioning control device has the following disadvantages.
First, when a head address is switched while the head is in a servo reference area (i.e., a burst-area) in a data recording area of a magnetic disk, it is not clear whether servo data latched in memory was read before or after the head address switching and thus servo information may become invalid and thus be cancelled. As a result of such cancellation of the incorrect servo information, the quantity of servo information necessary for accurate measurements of an amount of tracking error may not be read.
Second, since a microprocessor unit (MPU) is interposed between the magnetic head and the control device, when a sector period is changed in a cylinder area by referring to a cylinder address, a relatively long period of time is required for adjusting the sector period. Therefore, such a device may operate with a previous, and incorrect, sector period and burst-area information is attempted to be read out at a position of the disk which does not correspond to a burst-area, resulting in a degradation of the accuracy of tracking error measurement. For this reason, there is a degradation in head positioning control in conventional devices.